Medium-chain acyl-coenzyme A dehydrogenase (MCAD) deficiency is an inherited disorder that prevents your body from breaking down certain fats and turning them into energy. Your metabolism involves the processes your body uses to produce energy. MCAD deficiency can cause problems with your metabolism.

If left untreated, MCAD deficiency may lead to severe lack of energy and tiredness, liver disease, coma, and other serious health problems. Also, the level of sugar in your blood can drop dangerously low — a condition called hypoglycemia. Prevention and prompt treatment are essential regardless of blood sugar level. If you have MCAD deficiency, a sudden episode, called a metabolic crisis, can be caused by common illnesses, high fever, stomach problems or going too long without eating, known as prolonged fasting.

MCAD deficiency is present from birth and is a lifelong condition. In the United States, all states test for MCAD deficiency at birth as part of newborn screening. Many other countries also provide routine newborn screening for MCAD deficiency. If MCAD deficiency is diagnosed and treated early, the disorder can be well managed through diet and lifestyle.

MCAD deficiency is usually first identified in babies and young children. In rare cases, the disorder is not diagnosed until adulthood.

Symptoms can vary among people with MCAD deficiency. They may include:

• Vomiting.
• Low or no energy.
• Weak feeling.
• Low blood sugar.

A sudden severe episode, called a metabolic crisis, can be due to:

• Going too long without eating.
• Missing meals.
• Common infections.
• High fever.
• Ongoing stomach and digestive problems that may cause vomiting and diarrhea.
• Intense exercise.

When to see a doctor

In the United States and many other countries, newborn screening programs test for MCAD deficiency. After your first evaluation, you may be referred to a specialist in evaluating and treating MCAD deficiency. You may also be referred to other health care team members, such as a registered dietitian.

Contact your health care team if you've been diagnosed with MCAD deficiency and have a high fever, no appetite, stomach or digestive symptoms, or a planned medical procedure that requires fasting.

A child is at risk of MCAD deficiency if both parents are carriers of a gene known to cause it. The child then inherits two copies of the gene — one from each parent. Children who inherit only one copy of the affected gene from one parent typically won't develop MCAD deficiency but will be carriers of the gene.

If metabolic crisis caused by MCAD deficiency is left untreated, it can lead to:

• Seizures.
• Liver problems.
• Brain damage.
• Coma.
• Sudden death.

MCAD deficiency is diagnosed through newborn screening followed by genetic testing.

• Newborn screening. Many countries, including all states in the United States, screen for MCAD deficiency at birth. Using a heel prick, a few drops of your baby's blood are taken and analyzed. If screening levels are outside the standard range, additional testing can be done.
• Genetic testing. Genetic testing can reveal the changed gene that causes MCAD deficiency. Depending on the type of test, a sample of blood or saliva or cells from the inside of the cheek, the skin or other tissue is collected and sent to a lab to be tested. Your health care provider may also recommend testing family members for this gene. Genetic counseling can help you understand the testing process and what the results mean.

A metabolic specialist, and often a registered dietitian, are usually included in your diagnosis and treatment. Lab tests can be done to help identify problems with your metabolism — the processes your body uses to produce energy. Results can help treat or prevent complications.

Newborn screening at birth allows MCAD deficiency to be diagnosed and treated early, before symptoms occur, preventing complications. Once identified, the disorder can be managed through diet and lifestyle.

The main goal of treatment for MCAD deficiency is to prevent problems caused by your metabolism that can lead to low blood sugar. To maintain blood sugar levels and avoid hypoglycemia:

• Infants require frequent feedings that include getting enough calories from complex carbohydrates.
• Children and adults need to get enough complex carbohydrates on a regular schedule of meals and snacks.

Your health care team may recommend additional treatment options.

Work with your health care team, including a registered dietitian, to develop a treatment plan tailored to your energy needs. This includes planning for extra complex carbohydrates needed during illness, stress or increased activity.

Limit fasting

The length of time that is safe for fasting — going without eating — may vary with age and your health care teamꞌs recommendations. For example, during the first 4 months of life, well infants' fasting time may be no longer than two to three hours. Fasting time may be gradually increased up to 12 hours by 1 year of age. Children and adults should not fast for longer than 12 hours.

Prevent hypoglycemia

Recommendations to prevent low blood sugar called hypoglycemia generally include:

• Avoid fasting longer than recommended by your health care team.
• Eat regular meals and snacks with adequate calories from complex carbohydrates, such as brown bread, rice, pasta and cereal, for energy needs.
• Choose foods that are high in complex carbohydrates and lower in fat.
• Increase calories by eating extra complex carbohydrates during illness, stress or increased activity and before going to sleep.
• Limit alcohol use.

Treat hypoglycemia

Talk with your health care provider about what to do if symptoms of low blood sugar develop so that you have an emergency plan. Strategies may include:

• Taking simple carbohydrates, such as sugar (glucose) tablets or sweetened beverages, such as juice, that are not labeled "diet."
• Seeking emergency medical care if you can't eat or if you have diarrhea or vomiting. An intravenous (IV) line for extra glucose and additional treatment may be needed.

Parent and family understanding of the condition is critical to ongoing care and prevention of low blood sugar episodes and other complications. Prevention tips include:

• Avoid skipping meals.
• Eat complex carbohydrates before extra activity or exercise.
• Eat complex carbohydrates before going to bed.
• Increase calories with extra complex carbohydrates during illness or stress.
• Always carry complex carbohydrate snacks.
• Always carry a source of simple carbohydrates to treat low blood sugar.
• Know the warning signs of low blood sugar and other symptoms of a metabolic crisis.

If you or your child have MCAD deficiency, wear a medical alert bracelet or necklace and carry a medical card. This lets health care providers know of your condition, even in an emergency. Ask your health care provider about information for health professionals that you can carry with you in case emergency care is needed.

Caring for a child or family member with a lifelong disorder such as MCAD deficiency can be challenging. Consider these strategies:

• Learn about the disorder. Learn as much as you can about MCAD deficiency. Then you can make the best choices and be an advocate for yourself or your child. Help your child, family members, caregivers, teachers and friends understand the condition, the care needed and the consequences of not following dietary instructions.
• Find a team of trusted professionals. You'll need to make important decisions every day about care. Medical centers with specialty teams can offer you information about the disorder, as well as nutritional advice and support, and can help you manage care.
• Seek out other families. Talking to people who are dealing with similar challenges can give you information and emotional support. Ask your health care provider about support groups in your community. If a group isn't for you, maybe your provider can put you in touch with a family who has dealt with the disorder. Or you may be able to find a group or individual support online.
• Ask for help from family and friends. Ask for or accept help from family and friends in caring for your loved one when needed. Take time for your own interests and activities. Counseling with a mental health professional may help with adjustment and coping for you or your child.